Lycopene (also referred to as Ψ,Ψ-carotene) is one of the many carotenoids that exist in nature. Lycopene can be easily found in ripe tomato fruits, watermelons and pink grapefruits, giving them a characteristic red pigmentation. Lycopene obtained from raw tomatoes contains approximately 5% or more of cis-lycopene. According Schierle et al. 1997, lycopene obtained from raw tomatoes contains 94-96% of all-E-lycopene, 3-5% of 5Z-lycopene and a minor quantity of Z-isomers. Recent epidemiological studies show that lycopene as antioxidant may alleviate coronary heart disease and cancers of prostate, bladder, skin, digestive tract, breast and cervix.
Lycopene can be produced in two ways: extraction and synthesis. Biological lycopene is extracted either from fruits (such as tomatoes or watermelons) or from fungal biomass (such as Blakeslea trispora). Synthetic lycopene is manufactured through chemical synthesis. Lycopene produced by using synthesis process has lower all-E content than that extracted from B. trispora. The joint FAO (Food and Agriculture Organization of the United Nations)/WHO (World Health Organization) expert committee has established specifications for both synthetic lycopene and lycopene extracted from B. trispora at the 67th meeting of JECFA (2006). For synthetic lycopene, total lycopene content shall be higher than 96%, in which at least 70% must be all-E-lycopene and the remains are 5Z-lycopene and a minor quantity of Z-isomers. For lycopene extracted from B. trispora, the total lycopene content shall be higher than 95%, in which at least 90% must be all-E-lycopene and the remains are other carotenoids (β- and γ-carotene) for not more than 5%. These specifications indicate that lycopene extracted from B. trispora consists mainly of all-E-form, which no synthetic lycopene prepared using the nowadays technology may reach.
Pseudoionone is one of the starting materials for lycopene syntheses. It is a mixture of cis and trans isomers (also referred to as the cis/trans mixture). In general, pseudoionone cis/trans mixtures containing about 20% to 50% of all-trans-isomer and the remains of other cis-isomers are available in the market. A cis-pseudoionone will result in a cis-lycopene and an all-trans-pseudoionone will result in an all-E-lycopene, after the syntheses. In order to obtain higher all-E containing lycopene, a pseudoionone with higher all-trans content shall be used. Therefore, the all-trans-pseudoionone must first be separated from the pseudoionone cis/trans mixture before the syntheses. In the conventional technology, all-trans-pseudoionone is isolated from the cis/trans mixture by a fractional distillation operation. This purified all-trans-pseudoionone so obtained is then used to synthesize a C15 phosphonium salt to produce lycopene.
Unfortunately, the conventional synthesis process in producing the C15 phosphonium salts will cause a part of the all-trans-form to convert to cis-forms during the reaction. With the current technology, even the high all-E containing (90% to 95%) C15-OH (also referred to as 3,7,11-trimethyl-dodeca-1,4,6,10-tetraen-3-ol or vinyl-pseudoionol) is used, a product with only 65.2% to 71.1% of all-E-C15-Wittig salts, as well as 9.8% to 10.3% of 6Z and 8.2% to 10.8% of 2Z isomers, would be obtained. Clearly, the resulted products have lower E isomer/Z isomer ratios, which are about 3.4:1 to 3.8:1. Reference may be made to, for example, U.S. Pat. No. 6,603,045, U.S. Pat. No. 6,433,226, U.S. Pat. No. 6,187,959 and U.S. Pat. No. 2002/0,128,516. Such poor E/Z selectivity of C15 phosphonium salts is a challenge in producing a synthetic all-E-lycopene, with all-E content competitive to that of biological lycopenes extracted from natural sources such as B. trispora. 
The other method for producing synthetic all-E-lycopenes uses thermal isomerization process that converts Z-isomers of lycopene into all-E-lycopene. Reference may be made to U.S. Pat. No. 7,126,036 and U.S. Pat. No. 2004/0049082. This process increases the all-E content of the obtained lycopene from 53% to 73.4%-87.8%.
It has been found that all-E-C15-Wittig salts can be separated from the C15 phosphonium salt obtained from the reaction of cis/trans mixture, using a series of purification steps in aprotic solvents. According to the present invention, significantly high E/Z selectivity in the C15 phosphonium salts, with an E isomer/Z isomer ratio of greater than 15:1, may be realized. By reacting a C10-dialdehyde (also referred to as 2,7-dimethyl-2,4,6-octatriene-1,8-dial) with such high all-E content of C15-Wittig salts through a double Wittig reaction, a synthetic lycopene with all-E content for up to 95% may be produced. The obtained all-E content may even satisfy the all-E content specification for biological lycopenes. By switching the reactants from high all-E content of C15-Wittig salts to high 6Z content of C15 phosphonium salts, a synthetic lycopene with a 5Z-content of up to 97% is also obtained.